Because of their superior magnetic properties, silicon sheet steels are widely used in the production of magnetic core components in electrical equipment such as motors, generators, transformers and the like. These favorable magnetic properties, namely high magnetic permeability, high electrical resistance and low hysteresis losses, minimize wasteful conversion of electrical energy into heat, and will therefore permit the manufacture of electrical equipment having greater power and efficiency.
Silicon sheet steels are normally divided into two classifications; grain oriented steels and nonoriented steels. The grain oriented silicon sheet steels are produced under very carefully controlled composition and process parameters so that generally over 90 percent of the secondary recrystallized grains exhibit a (110)[001] texture as described in U.S. Pat. No. 2,867,558, May. Because of this preferred orientation, the magnetic properties of such sheet steels are far superior in the direction parallel to the rolling direction, as compared to all other directions. This anisotropic characteristic makes sheet steels ideally suited as core material for stationary electrical equipment such as distribution transformers, because the core can be manufactured such that full advantage can be taken of the superior directional magnetic properties.
In the case of rotating electrical equipment, such as motors and generators, the magnetic properties must be reasonably uniform in all directions, and hence grain oriented sheet steels are not used therein. For these applications, the nonoriented sheet steels are produced, wherein very carefully controlled processing parameters are employed to optimize a random orientation of the steel grains, and thus optimize isotropic magnetic properties. Also, the nonoriented silicon steels exhibit a primary-recrystallized microstructure, a smaller grain size, and a rather weak texture as compared with grain oriented silicon steel. Because of the random orientation, the magnetic properties of a nonoriented sheet steel are not as good in the rolling direction as they are in oriented steels particularly at high flux densities.
In electrical equipment, such as ballast transformers or constant-voltage transformers employing an "I," "E" or "U" type laminations in the cores, it is essential to have good magnetic properties in both the rolling direction and the direction perpendicular thereto. Therefore, nonoriented silicon sheet steels are used in these transformers. Nevertheless, a number of manufacturers of such transformers prefer to avoid completely isotropic magnetic properties. That is, they desire an electrical sheet having somewhat enhanced magnetic properties in the rolling direction or main flux direction. In view of the fact that cold rolling a steel does tend to promote some degree of grain orientation in the rolling direction, a completely random orientation is perhaps not achievable in a cold rolled product as indicated in U.S. Pat. No. 3,203,839, Takahashi. Accordingly, even those silicon sheet steels classified as nonoriented are characterized by some degree of orientation, and hence slightly superior magnetic properties in the rolling direction. In the past therefore, it has not been difficult to satisfy those manufacturers who required nonoriented silicon sheet steel having somewhat superior magnetic properties in the rolling direction. Now, however, several such manufacturers are specifying minimum permeability values in the rolling direction, in addition to the usual core-loss requirements, which is difficult to achieve especially in the thinner gages, such as 29-gage. Of course, the grain oriented grades can readily meet the permeability requirements in the rolling direction, but these grades are much too costly to produce for use in these applications.